capabilities. Basically, separation and/or preconcen-tration are needed when one of the following situations occurs: concentration of analyte is below the sensitivity of the instrumental method; interferences exist in the sample (relative to the instrument to be used); or physical or chemical states of the sample are not appropriate for the instrument. Sensitivities for elements varies with the instrumental method and are relative to matrix type; however, a general listing of sensitivities of commonly used analytical equipment is given in Table 1.

The impetus for doing an extraction will therefore depend on the availability of instruments and the capability of the instrument relative to the matrix type (i.e. interferences). Inorganic extraction schemes are typically instrument specific. Although instrument development has significantly reduced detection limits, availability of some of the more state-of-the-art equipment is still limited to specialized or well-equipped laboratories. The need for separation and preconcentration therefore still exist. Speciation studies will also continue to support development and research into inorganic separations from complex matrices.

Because atomic absorption spectrometry (AAS) is readily available, but the detection limits are high in relation to today's needs, there are numerous solvent extraction methods available for metals in AAS analysis. Several excellent sources are listed in Further Reading; these have lengthy tables of inorganic extraction schemes.

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